1. Field of the Invention
The invention relates to a process and a device for the discharge of residues occurring during the gasification of ash-containing fuels, in particular solid fuels such as bituminous coal, lignite and other carbonaceous substances with oxygen or oxygen-containing compounds such as water and/or carbon dioxide. The feedstock is converted at a pressure of 10 to 20 bar. The gasification residues leave the gasification chamber in liquid or plastic form and are turned into a solid granulate--which can also be finely grained--in a water bath which is connected to the gasification chamber. With the aid of a water-filled lock vessel which is located under the water bath, the granulate residues are periodically discharged from the pressure system of the pressurized gasification plant.
2. Discussion of Prior Art
A process and a device for the discharge of ash must fulfil a number of demands. Apart from the fact that the system should be economically viable to operate, it must be ensured that the residues are removed safely and without any detrimental effect on the environment. Thus the escape of product gas from the high-pressure gasification chamber into the atmosphere must be avoided at all costs owing to the danger of poisoning and explosion. Moreover, it must be ensured that dangerous and/or odorous gases, which for example are dissolved in the process water under pressure and released when the pressure is reduced, as wel as the polluted water, which is led off with the slag, are prevented from entering the environment. Finally, the flow of the granulated slag from the gasification chamber into the discharging system must only be interrupted by the discharging process for a short period to avoid slag building up in the gasification chamber and blocking the outlet.
In the DE-OS No. 28 29 629 corresponding to U. S. applicaton Ser. No. 280,029, now U.S. Pat. No. 4,425,139 assigned to the assignee hereof, the disclosure of which is hereby incorporated herein by reference, a process is described for the periodic discharge of residues occurring during the gasification of ash-containing fuels. The combustion residues occurring are granulated in a water bath in this process. Underneath the water bath a lock vessel is located which is connected to a separate water supply. It is connected to the water bath via a line in which an injector is installed. The injector sucks the water out of the lock vessel and returns it to the water bath. To compensate for this, water and slag enter the lock vessel from the water bath. The slag forms sediment in the lock vessel. Before the slag which has collected in the lock vessel is removed, the lock vessel which is under the same pressure as the water bath is depressurized into the separate water supply which is either pressureless or under slight excess pressure. Subsequently, a predetermined amount of water is flushed from the water supply into the lock vessel whereby the water and slag leave the lock vessel and enter a downstream collecting vessel which is either pressureless or under slight excess pressure. The water and slag are separated in the collecting vessel. After the connection between the lock vessel and the water bath has been shut off the lock vessel which is at all times completely filled with water, is brought to the same pressure as that of the water bath by the opening of a connecting line which leads to the water bath. The lock vessel is filled with slag by means of the water circuit previously described which is maintained by the injector.
The process described in the afore-mentioned publication can only operate trouble-free if the temperature in the water bath can be kept under 100.degree. C. if possible or only slightly above the boiling point of the aqueous phase at atmospheric pressure. At temperatures above the boiling point of the aqueous phase at atmospheric pressure difficulties owing to spontaneous undesired vaporisation occur during the reduction of the pressure of the lock vessel to atmospheric pressure which must precede the pressureless emptying procedure. This vaporization prevents the desired rapid depressurization and stirs up liquid and already deposited ash which is carried off with the flash gas.
When coal with a high slag content is used where the slag enters the water bath in a hot state and/or when the slag mixture formed from the coal is partly or directly quenched, the water bath is automatically heated to temperatures far above the boiling point of the aqueous phase at atmospheric pressure depending on the operating pressure. This causes the difficulties which have already been described above. These disadvantages are eliminated by the present invention.